The present invention relates to a novel shielding material of electromagnetic waves or, more particularly, to a shielding material of electromagnetic waves formed of a polymeric matrix and an electroconductive particulate dispersant dispersed therein.
One of the serious problems accompanying the recent development and prevalence of various kinds of electronic instruments is the electromagnetic noise caused by the interference of the electromagnetic or radio waves emitted from an instrument with others as a public nuisance. A method for preventing or reducing such a trouble is the use of a shielding material of radio waves and it is a very important and urgent problem to develop an efficient and inexpensive material for such a purpose.
Several types of radio wave shielding materials are known in the art including a material prepared by providing an electroconductive surface layer on a suitable substrate material by, for example, flame fusion of a metal or coating with an electroconductive coating composition, e.g. paint. These shielding materials are, however, not quite satisfactory from the practical standpoint due to the expensiveness and poor durability of the shielding effect. An alternative shielding material is formed of a polymeric material; i.e. plastic resins and rubbers, as a matrix and a conductive particulate or fibrous dispersant uniformly dispersed in the matrix. Metal fibers and metal powders are hitherto proposed as such a conductive dispersant. A problem in the shielding material of a polymeric matrix impregnated with such a metallic dispersant is the decreased moldability of the polymeric composition and the insufficient mechanical strengths of the shaped shielding material when the polymeric matrix material is impregnated with the metallic dispersant in an amount sufficient to ensure effective shielding effect of radio waves. Therefore, the fields of application of the shielding materials of such a type is largely limited.